1. Infection of human rectosigmoid and tonsillar tissues by CCR5- and CXCR4-using HIV-1[unreadable] Irrespective of the route of transmission, acute infection is associated with R5 HIV-1. The mechanism and the cause of selective R5 transmission and its early dominance are not fully understood and probably consist of several sequential and parallel selective barriers (gatekeepers). Recently, a strong emphasis has been given to the role of gut-associated lymphoid tissue (GALT), which was thought to be one of these selective barriers. To study mechanisms of this selection, we used a system of intestinal explants derived from both biopsies and surgical resection specimens. In this system, under controlled laboratory conditions, we asked whether GALT is more vulnerable to R5 than to X4 HIV-1 and compared infection of rectosigmoid tissue with infection of tonsillar tissue by these two HIV-1 variants. Relative level of R5 replication in rectosigmoid tissue was much greater than in tonsillar tissue. The most evident explanation for this is the large difference in the presence of CCR5+ CD4 T cells (70% in GALT compared to about 15% in tonsils). Furthermore, tonsillar tissue responds to X4 HIV-1 infection by upregulating the secretion of CC-chemokines, providing a potential CCR5 blockade and hence a further resistance to R5 infection, whereas rectosigmoid tissue failed to increase such innate immune responses. Thus, rectosigmoid is more prone to R5 HIV-1 infection than tonsillar tissue, primarily because of the prevalence of R5 cell targets and reduced chemokine blockade. Nevertheless, the majority of CD4 T cells express CXCR4 and X4 HIV-1 readily replicates in both tissues, suggesting that the differential expression of co-receptors is one of the gatekeepers of HIV-1 infection that must be complemented by other barriers to account for the selective R5 infection of the rectal mucosa in vivo. [unreadable] [unreadable] 2. Activation of lymphoid tissue as a driving force for HIV infection [unreadable] HIV-induced tissue immune hyper-activation accompanied by cytokine secretion seems to be the centerpiece of CD4 T cell depletion, redistribution and sequestration of various lymphocyte subpopulations characteristic of HIV-1 disease. To address mechanisms of these phenomena we compared cytokine expression spectra and distributions of T cell subsets in lymph nodes from chronically HIV-1 infected patients with those from healthy controls. We found a reduction of the fraction of CD4+ T cells in lymph nodes from HIV-1 infected patients associated with increased effector T cell frequencies and a profound upregulation of the activation marker, CD38, in naive, central memory, and effector CD4+ and CD8+ T cells. Likewise, the death receptor Fas (CD95) was more frequently detectable on T cells from HIV-1 infected nodes. Cytokine dysregulation was evident with 2-to-3 log upregulation of IL-2 and IL-15 release as well as with an increased secretion of IL-10 and IL-1beta in infected lymph nodes. We propose that the deterioration of the lymph node structure and function in the course of chronic HIV-1 infection is a complex phenomenon including the death of infected cells and the activation of other cells, both infected and uninfected. In this setting, activated effector cells are excessively attracted or retained in infected nodes and serve as a source of cytokines, which in turn may activate new cells leading to a massive activation of lymphoid tissue. In the case of chronic HIV-1 infection this phenomenon leads to the lymphadenopathy and massive bystander activation resulting in a massive death of T cells and dendritic cells that characterize HIV-1 infection. To reveal mechanisms connecting cell activation and acute HIV-1 infection under controlled laboratory conditions, we inoculated blocks of human tonsillar tissue with HIV-1 and analyzed T cell activation status. HIV-1 load in this system depends on the number of activated target cells, specifically those of CD25+/HLA-DR+ phenotype. HIV-1 infection of lymphoid tissue was associated with activation of both HIV-1-infected and uninfected (bystanders) T cells and remarkably, HIV-1 infection seems to facilitate the very same pattern of lymphoid tissue activation that is associated with enhanced HIV-1 replication. HIV-1 infection of these tissues was followed by CD4+ T cell apoptosis that was selectively increased in infected cells expressing CD25/HLA-DR. [unreadable] Thus, in human lymphoid tissue, HIV-1 induces a vicious circle of infection of activated cells, driving them into apoptosis and triggering cytokine dysregulation leading to activation of uninfected cells that makes them susceptible to productive HIV infection, and inappropriately attracts and/or retains these cells in lymphoid tissue. Targeting individual elements of this cycle may constitute new anti-HIV-1 strategies. [unreadable] [unreadable] 3. Effect of non-HIV pathogens on HIV infection in human lymphoid tissue [unreadable] We continue to study the effects of non-HIV pathogens on HIV infection in human lymphoid tissue. The study of interactions between vaccinia virus (VACV) and HIV is of particular clinical relevance in view of possible anti-poxvirus immunizations of HIV-infected subjects, and of the use of vaccinia as a vector to deliver anti-HIV vaccine. VACV readily infects both T and B lymphocytes in the context of human tissues and equally depletes either cell type. Among T lymphocytes, CD8+ cells are preferentially depleted because they are preferentially infected. T cells expressing CCR5 or the activation markers CD25, CD38, and HLA-DR are other major targets for VACV infection. Since CCR5 is one of the two HIV coreceptors, the effect of VACV on CCR5-expressing cells causes these two viruses to enter into complex interactions in co-infected individuals. Because of VACV-induced CCR5 downregulation and depletion of activated CCR5-expressing cells at the principal site of productive HIV-1 infection, R5 but not X4 replication was dramatically inhibited. [unreadable] Measles virus (MV) is another pathogen that was reported by us and others to interact with HIV in coinfected tissues. We infected ex vivo human tonsillar tissue with either wild-type MVs or vaccine strains. MV preferentially infected B lymphocytes. Cells that express the MV receptor signaling lymphocyte activation molecule (SLAM, CD150) are preferentially infected by all wild-type MV strains. Memory T lymphocytes expressing high levels of SLAM are infected by wild-type MVs about five times more efficiently than naive T lymphocytes that do not express SLAM. The vaccine strain, however, does not discriminate between memory and naive T lymphocytes. Depletion of SLAM-expressing T lymphocytes is more marked than that of other SLAM-expressing lymphoid cells. These results give new insights into the mechanisms of MV-induced immune suppression and vaccine attenuation. Furthermore, the preferential infection and depletion of activated T cells by wild type MV provides a new insight into the mechanism by which MV infection suppresses HIV replication in regions where both viruses are endemic. Thus, the study of VAC, and MV, together with earlier reported studies of human herpesviruses 6 and 7, revealed diverse mechanisms of HIV interactions with non-HIV viruses including competition for activated T cells, in particular for CCR5-expressing CD4 T cells, downregulation of HIV receptors and coreceptors, upregulation of chemokines, and depletion of target cells. Mimicking non-HIV pathogens (HHV-7)-induced CD4 downregulation with cyclotriazadisulfonamide (CADA) resulted in significant suppression of HIV-1 infection in human lymphoid tissue ex vivo. Simulation of such phenomenon with (inactivated) pathogens, their components or other compounds may be an important strategy in suppressing HIV-1.